Repair Topics > > Serpentine Belt versus Timing Belt: Understanding the Difference
Learn the difference between a Serpentine belt versus timing belt
They’re often confused, but there’s a huge difference between a serpentine belt versus a timing belt. While both are essential components, they serve different purposes and require distinct maintenance approaches. This article will explore the functions, differences, and maintenance needs of serpentine belts verus timing belts.
What a serpentine belt does
A serpentine belt drives accessory components like the alternator, water pump, power steering pump, smog pump, and AC compressor. It is driven by the harmonic balancer located on the front of the engine and tensioned by a manual or automatic tensioner. It’s referred to as a serpentine belt because it snakes around the driven components, driving some with multiple “V” ribs and others with the smooth backside of the belt.
This image shows a serpentine belt mounted on the front of an engine. Notice how the belt snakes around the components, driving some with the ribbed side of the belt and others with the smooth backside of the belt
Modern serpentine belts are made of durable rubber compounds reinforced with fiber cords. They feature a flat side that contacts the pulleys and a grooved side that provides grip and helps dissipate heat.
You can usually spot the serpentine belt easily when you open your car’s hood. It’s visible on the front of the engine, winding around several pulleys.
What a timing belt does
The timing belt, also called a cambelt, synchronizes the rotation of the crankshaft and camshaft(s), ensuring that the engine’s valves open and close at the proper times during each cylinder’s intake and exhaust strokes.
A sprocket or clogged wheel drives a timing belt from the front end of the crankshaft. You can’t see a timing belt under the hood because it is always covered with a timing belt cover. You’d have to remove the timing belt cover to examine it. Timing belts typically run without lubrication, except in special applications where the belt is made of a different material that can withstand submersion in engine oil.
The image below shows a timing belt on a Subaru boxer engine. The belt is driven by a cogged crankshaft pulley and tensioned by a hydraulic belt tensioner. It then wraps around the camshafts using the toothed portion of the belt and drives the water pump off the smooth backside of the belt.
Subaru timing belt routing
This image shows a typical timing belt with lateral cogs on one side of the belt
Serpentine belt versus a timing belt — Appearance
A serpentine belt is composed of multiple rows of small “V’s” that mesh with corresponding “V’s” in the pulleys.
A timing belt is composed of lateral cogs instead of “V”s”.
Serpentine belt construction
A serpentine belt is made from Ethylene Polypropylene Diene (EPDM) and other high-tech materials. EPDM is heat and crack-resistant and provides higher resistance to vehicle fluids and oxidation than older neoprene elastomeric materials.
The belt is constructed with stretch-resistant embedded tensile cords, usually made from aramid. The multi-ribbed side of the belt incorporates multiple “V” profiles that mate with corresponding channels in the component pulleys. The “V” profiles provide the “traction” to rotate the driven components.
The flat backside of the belt has an embedded fabric material to drive flat pulleys and resist wear
Notice the linear rows of ribs that correspond to the tensile cord embedded in the rubber
Timing Belt Construction
Timing belts are precision components made through a multi-step process. The base material is typically a high-strength rubber compound, often HNBR (Hydrogenated Nitrile Butadiene
This is an example of a double-sided timing belt
Rubber) or EPDM (Ethylene Propylene Diene Monomer). The reinforcing fibers are made from fiberglass or Kevlar and embedded into the rubber, typically running the length of the belt for strength.
The belt is placed into a mold that forms the teeth on one side. Heat and pressure are applied to cure the rubber and set the tooth shape. Tooth profiles are precisely engineered to match specific engine designs.
In some applications, cogs are molded into both sides of the belt.
Serpentine belt versus polygroove belt— there’s a difference
To qualify as a serpentine belt, the belt must drive engine components from both the ribbed
and backside of the belt. All serpentine belts are tensioned with an automatic belt tensioner that cannot be adjusted.
A polygroove belt is often mistaken for a serpentine belt because it looks like one. However, a polygroove belt is designed to drive components only from the ribbed side of the belt, not the backside.
A timing belt has deep, horizontal ribbing.Whereas, a serpentine belt has thinner grooves that run vertically. If you drive an older, high-mileage vehicle, you should be extra careful with these belts. Eventually, they will need to be changed.
A timing belt has horizontal “teeth” designed to fit the cogwheels of the crankshaft and camshaft.A serpentine belt has V-shaped grooves that run vertically along the belt.
If we are inspecting our vehicle, or we are about to make a visit to the garage, the first sign that will indicate that the belt is worn is its appearance. It is possible to see small cracks throughout the entire piece. If the cracks are enlarged, then the internal threads of the cracks can be seen.
Whether you go to the mechanic or do it yourself, replacing a serpentine belt costs $58 to $126. The price of a serpentine belt starts at around $25 and goes up to $75 at most. It typically takes about an hour to replace the serpentine belt, and if you know some car repair basics, you could change the belt yourself.
What does a serpentine belt sound like when it's going bad? You may hear squealing or chirping if the belt is in the early stages of going bad, or it could progress to a slapping or knocking noise if portions of the belt are torn and flapping around under the hood.
Other signs of a failing Timing Belt may include excessive engine vibrations, ticking or clanking noises coming from the front of the engine, and the Check Engine light coming on.
With it removed, you're looking for frayed edges or damage, perhaps worn teeth on the inside of the belt. If the rubber looks to be shiny or marbled, that's another sign it's getting old, along with signs of cracking within the rubber.
The camshaft works the cylinder head valve and rocker arms, to send fuel to the combustion chamber. The ejected gases pass through the exhaust manifold. So, when the timing belt begins to weaken or breaks, a ticking noise is heard from inside the engine.
A timing belt has horizontal "teeth" that are made to fit both the crankshaft and camshaft.In contrast, a serpentine belt has multiple V-shaped grooves that appear vertically along the belt. Over time, these belts need to be replaced (roughly around the same time).
Look for a sticker on the belt cover or remove the upper belt cover and inspect the belt for cracks , glazing, the belt makings being worn off. Look in the Car receipts or service history. Water Pump. A lot less expensive than replacing the whole engine if the Timing Belt snaps.
Some signs are much more obvious, such as cracking or fraying. Belts with that kind of damage should be replaced immediately. A further way to check is to press a fingernail or the tip of a screwdriver gently onto the belt. If the pressure does not leave a mark, it means the rubber is becoming too stiff.
First, the camshaft stops moving, and all timing is lost. Then, the pistons crash into the valves, damaging both parts. Depending on how hard the pistons and valves collide, you might also end up with decimated cylinder walls. The broken timing belt basically takes out this entire portion of the engine.
If you've acquired a new car and you're wondering if the cam belt was recently replaced, you can always check the maintenance records (if these have been provided with the car). The maintenance records should also indicate the date of the replacement and how many miles the car has done since it's been fitted.
Comparatively, replacing your timing belt is inexpensive, though its full cost will depend on a variety of factors, such as the engine type, maintenance, driving conditions and more. According to our experts, the average timing belt replacement cost will range between $400 and $1,000.
A failing timing belt may cause a myriad of symptoms, such as unusual noises coming from under the hood, engine misfires, and poor engine performance. In most cases, if the timing belt fails, the engine will not run at all, and the engine can not be restarted without replacing the timing belt.
Introduction: My name is Aracelis Kilback, I am a nice, gentle, agreeable, joyous, attractive, combative, gifted person who loves writing and wants to share my knowledge and understanding with you.
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